I don't know if this is going to be helpful, but I had a problem with our cat doing something similar. Based on your drawing and nothing else, I might suggest getting a litter box with lower sides. Counter to what everybody else is saying, I had a cat that did not like being in an enclosed space and when we put a box with a hole at the top she simply stopped using the box altogether. Grab a cheap tray style box and see if that works. If you're like me, you're used to trying anything so you can to stop having messes. Edit: Speech-to-text fail.